The Kidney and Osmoregulation (homeostasis chapter 6)

Question 1

Osmoregulation

Answer 1

• The balancing and control of the water potential of the blood
• The amount of water lost in the urine is controlled ADH in a negative feedback system

Question 2

Where is ADH produced and secreted into?

Answer 2

ADH is produced in the hypothalamus and secreted into the posterior pituitary gland (where it is stored)

Question 3

What is the effect of ADH on the distal convoluted tubule and the collecting duct?

Answer 3

It increases the permeability of the distal convoluted tubule and the collecting duct to water

Question 4

Mechanisms of ADH action

Answer 4

• ADH binds to receptors on the cell surface membrane and triggers the formation of cAMP as a second messenger inside the cell - cAMP relays the signals received at the cell surface receptors to molecules inside the cell
• cAMP causes a cascade of events to happen:
  1. Vesicles lining the cells lining the collecting duct fuse with the cell surface membranes on the side of the cell in contact with the tissue fluid of the medulla
  2. The membranes of these vesicles contain protein-based water channels (aquaporins) and when they are inserted into the cell surface membrane, they make it permeable to water
  3. This provides a route for water to move out of the tubule cells into the tissue fluid of the medulla and the blood capillaries by osmosis